Revert 97446 - Modifying prefetch to account for multi-profile.

chrome/browser/net/predictor.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/net/predictor.h"
 
 #include <algorithm>
 #include <cmath>
 #include <set>
 #include <sstream>
 
-#include "base/bind.h"
-#include "base/command_line.h"
 #include "base/compiler_specific.h"
 #include "base/metrics/histogram.h"
-#include "base/stl_util.h"
 #include "base/stringprintf.h"
-#include "base/synchronization/waitable_event.h"
 #include "base/time.h"
 #include "base/values.h"
-#include "chrome/browser/io_thread.h"
 #include "chrome/browser/net/preconnect.h"
-#include "chrome/browser/prefs/browser_prefs.h"
-#include "chrome/browser/prefs/pref_service.h"
-#include "chrome/browser/prefs/scoped_user_pref_update.h"
-#include "chrome/browser/prefs/session_startup_pref.h"
-#include "chrome/common/chrome_switches.h"
-#include "chrome/common/pref_names.h"
 #include "content/browser/browser_thread.h"
 #include "net/base/address_list.h"
 #include "net/base/completion_callback.h"
 #include "net/base/host_port_pair.h"
 #include "net/base/host_resolver.h"
 #include "net/base/net_errors.h"
 #include "net/base/net_log.h"
 #include "net/base/single_request_host_resolver.h"
 
 using base::TimeDelta;
@@ skipping 18 matching lines @@
 // static
 const double Predictor::kReferrerTrimRatio = 0.97153;
 
 // static
 const TimeDelta Predictor::kDurationBetweenTrimmings = TimeDelta::FromHours(1);
 // static
 const TimeDelta Predictor::kDurationBetweenTrimmingIncrements =
     TimeDelta::FromSeconds(15);
 // static
 const size_t Predictor::kUrlsTrimmedPerIncrement = 5u;
-// static
-const size_t Predictor::kMaxSpeculativeParallelResolves = 3;
-// To control our congestion avoidance system, which discards a queue when
-// resolutions are "taking too long," we need an expected resolution time.
-// Common average is in the range of 300-500ms.
-const int kExpectedResolutionTimeMs = 500;
-// static
-const int Predictor::kTypicalSpeculativeGroupSize = 8;
-// static
-const int Predictor::kMaxSpeculativeResolveQueueDelayMs =
-    (kExpectedResolutionTimeMs * Predictor::kTypicalSpeculativeGroupSize) /
-    Predictor::kMaxSpeculativeParallelResolves;
-
-static int g_max_queueing_delay_ms = 0;
-static size_t g_max_parallel_resolves = 0u;
-
-// A version number for prefs that are saved. This should be incremented when
-// we change the format so that we discard old data.
-static const int kPredictorStartupFormatVersion = 1;
 
 class Predictor::LookupRequest {
  public:
   LookupRequest(Predictor* predictor,
                 net::HostResolver* host_resolver,
                 const GURL& url)
       : ALLOW_THIS_IN_INITIALIZER_LIST(
             net_callback_(this, &LookupRequest::OnLookupFinished)),
         predictor_(predictor),
         url_(url),
@@ skipping 26 matching lines @@
 
   Predictor* predictor_;  // The predictor which started us.
 
   const GURL url_;  // Hostname to resolve.
   net::SingleRequestHostResolver resolver_;
   net::AddressList addresses_;
 
   DISALLOW_COPY_AND_ASSIGN(LookupRequest);
 };
 
-Predictor::Predictor(bool preconnect_enabled)
-    : initial_observer_(NULL),
-      predictor_enabled_(true),
-      peak_pending_lookups_(0),
+Predictor::Predictor(net::HostResolver* host_resolver,
+                     TimeDelta max_dns_queue_delay,
+                     size_t max_concurrent,
+                     bool preconnect_enabled)
+    : peak_pending_lookups_(0),
       shutdown_(false),
-      max_concurrent_dns_lookups_(g_max_parallel_resolves),
-      max_dns_queue_delay_(
-          TimeDelta::FromMilliseconds(g_max_queueing_delay_ms)),
-      host_resolver_(NULL),
+      max_concurrent_dns_lookups_(max_concurrent),
+      max_dns_queue_delay_(max_dns_queue_delay),
+      host_resolver_(host_resolver),
       preconnect_enabled_(preconnect_enabled),
       consecutive_omnibox_preconnect_count_(0),
-      next_trim_time_(base::TimeTicks::Now() + kDurationBetweenTrimmings) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+      next_trim_time_(base::TimeTicks::Now() + kDurationBetweenTrimmings),
+      ALLOW_THIS_IN_INITIALIZER_LIST(trim_task_factory_(this)) {
 }
 
 Predictor::~Predictor() {
-  // TODO(rlp): Add DCHECK for CurrentlyOn(BrowserThread::IO) when the
-  // ProfileManagerTest has been updated with a mock profile.
   DCHECK(shutdown_);
 }
 
-// static
-Predictor* Predictor::CreatePredictor(
-    bool preconnect_enabled, bool simple_shutdown) {
-  if (simple_shutdown)
-    return new SimpleShutdownPredictor(preconnect_enabled);
-  return new Predictor(preconnect_enabled);
+void Predictor::Shutdown() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
+  DCHECK(!shutdown_);
+  shutdown_ = true;
+
+  std::set<LookupRequest*>::iterator it;
+  for (it = pending_lookups_.begin(); it != pending_lookups_.end(); ++it)
+    delete *it;
 }
 
-void Predictor::RegisterUserPrefs(PrefService* user_prefs) {
-  user_prefs->RegisterListPref(prefs::kDnsPrefetchingStartupList,
-                               PrefService::UNSYNCABLE_PREF);
-  user_prefs->RegisterListPref(prefs::kDnsPrefetchingHostReferralList,
-                               PrefService::UNSYNCABLE_PREF);
+// Overloaded Resolve() to take a vector of names.
+void Predictor::ResolveList(const UrlList& urls,
+                            UrlInfo::ResolutionMotivation motivation) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
+
+  for (UrlList::const_iterator it = urls.begin(); it < urls.end(); ++it) {
+    AppendToResolutionQueue(*it, motivation);
+  }
 }
 
-// --------------------- Start UI methods. ------------------------------------
-
-void Predictor::InitNetworkPredictor(PrefService* user_prefs,
-                                     PrefService* local_state,
-                                     IOThread* io_thread) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-
-  predictor_enabled_ = user_prefs->GetBoolean(prefs::kNetworkPredictionEnabled);
-
-  // Gather the list of hostnames to prefetch on startup.
-  UrlList urls = GetPredictedUrlListAtStartup(user_prefs, local_state);
-
-  base::ListValue* referral_list =
-      static_cast<base::ListValue*>(user_prefs->GetList(
-          prefs::kDnsPrefetchingHostReferralList)->DeepCopy());
-
-  // Remove obsolete preferences from local state if necessary.
-  int current_version =
-      local_state->GetInteger(prefs::kMultipleProfilePrefMigration);
-  if ((current_version & browser::DNS_PREFS) == 0) {
-    local_state->RegisterListPref(prefs::kDnsStartupPrefetchList,
-                                  PrefService::UNSYNCABLE_PREF);
-    local_state->RegisterListPref(prefs::kDnsHostReferralList,
-                                  PrefService::UNSYNCABLE_PREF);
-    local_state->ClearPref(prefs::kDnsStartupPrefetchList);
-    local_state->ClearPref(prefs::kDnsHostReferralList);
-    local_state->SetInteger(prefs::kMultipleProfilePrefMigration,
-        current_version | browser::DNS_PREFS);
-  }
-
-  BrowserThread::PostTask(
-      BrowserThread::IO,
-      FROM_HERE,
-      base::Bind(
-          &Predictor::FinalizeInitializationOnIOThread,
-          base::Unretained(this),
-          urls, referral_list,
-          io_thread));
+// Basic Resolve() takes an invidual name, and adds it
+// to the queue.
+void Predictor::Resolve(const GURL& url,
+                        UrlInfo::ResolutionMotivation motivation) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
+  if (!url.has_host())
+    return;
+  AppendToResolutionQueue(url, motivation);
 }
 
+void Predictor::LearnFromNavigation(const GURL& referring_url,
+                                    const GURL& target_url) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
+  DCHECK_EQ(referring_url, Predictor::CanonicalizeUrl(referring_url));
+  DCHECK_NE(referring_url, GURL::EmptyGURL());
+  DCHECK_EQ(target_url, Predictor::CanonicalizeUrl(target_url));
+  DCHECK_NE(target_url, GURL::EmptyGURL());
+
+  referrers_[referring_url].SuggestHost(target_url);
+  // Possibly do some referrer trimming.
+  TrimReferrers();
+}
+
+enum SubresourceValue {
+  PRECONNECTION,
+  PRERESOLUTION,
+  TOO_NEW,
+  SUBRESOURCE_VALUE_MAX
+};
+
 void Predictor::AnticipateOmniboxUrl(const GURL& url, bool preconnectable) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-  if (!predictor_enabled_)
-    return;
-  if (!url.is_valid() || !url.has_host())
-    return;
   std::string host = url.HostNoBrackets();
   bool is_new_host_request = (host != last_omnibox_host_);
   last_omnibox_host_ = host;
 
   UrlInfo::ResolutionMotivation motivation(UrlInfo::OMNIBOX_MOTIVATED);
   base::TimeTicks now = base::TimeTicks::Now();
 
   if (preconnect_enabled()) {
     if (preconnectable && !is_new_host_request) {
       ++consecutive_omnibox_preconnect_count_;
@@ skipping 43 matching lines @@
     const int kMinPreresolveSeconds(10);
     if (kMinPreresolveSeconds > (now - last_omnibox_preresolve_).InSeconds())
       return;
   }
   last_omnibox_preresolve_ = now;
 
   // Perform at least DNS pre-resolution.
   BrowserThread::PostTask(
       BrowserThread::IO,
       FROM_HERE,
-      base::Bind(&Predictor::Resolve, base::Unretained(this),
-                 CanonicalizeUrl(url), motivation));
+      NewRunnableMethod(this, &Predictor::Resolve, CanonicalizeUrl(url),
+                        motivation));
 }
 
 void Predictor::PreconnectUrlAndSubresources(const GURL& url) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-  if (!predictor_enabled_)
-    return;
-  if (!url.is_valid() || !url.has_host())
-    return;
   if (preconnect_enabled()) {
     std::string host = url.HostNoBrackets();
     UrlInfo::ResolutionMotivation motivation(UrlInfo::EARLY_LOAD_MOTIVATED);
     const int kConnectionsNeeded = 1;
     PreconnectOnUIThread(CanonicalizeUrl(url), motivation,
                          kConnectionsNeeded);
     PredictFrameSubresources(url.GetWithEmptyPath());
   }
 }
 
-UrlList Predictor::GetPredictedUrlListAtStartup(
-    PrefService* user_prefs,
-    PrefService* local_state) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-  UrlList urls;
-  // Recall list of URLs we learned about during last session.
-  // This may catch secondary hostnames, pulled in by the homepages.  It will
-  // also catch more of the "primary" home pages, since that was (presumably)
-  // rendered first (and will be rendered first this time too).
-  const ListValue* startup_list =
-      user_prefs->GetList(prefs::kDnsPrefetchingStartupList);
-
-  if (startup_list) {
-    base::ListValue::const_iterator it = startup_list->begin();
-    int format_version = -1;
-    if (it != startup_list->end() &&
-        (*it)->GetAsInteger(&format_version) &&
-        format_version == kPredictorStartupFormatVersion) {
-      ++it;
-      for (; it != startup_list->end(); ++it) {
-        std::string url_spec;
-        if (!(*it)->GetAsString(&url_spec)) {
-          LOG(DFATAL);
-          break;  // Format incompatibility.
-        }
-        GURL url(url_spec);
-        if (!url.has_host() || !url.has_scheme()) {
-          LOG(DFATAL);
-          break;  // Format incompatibility.
-        }
-
-        urls.push_back(url);
-      }
-    }
-  }
-
-  // Prepare for any static home page(s) the user has in prefs.  The user may
-  // have a LOT of tab's specified, so we may as well try to warm them all.
-  SessionStartupPref tab_start_pref =
-      SessionStartupPref::GetStartupPref(user_prefs);
-  if (SessionStartupPref::URLS == tab_start_pref.type) {
-    for (size_t i = 0; i < tab_start_pref.urls.size(); i++) {
-      GURL gurl = tab_start_pref.urls[i];
-      if (!gurl.is_valid() || gurl.SchemeIsFile() || gurl.host().empty())
-        continue;
-      if (gurl.SchemeIs("http") || gurl.SchemeIs("https"))
-        urls.push_back(gurl.GetWithEmptyPath());
-    }
-  }
-
-  if (urls.empty())
-    urls.push_back(GURL("http://www.google.com:80"));
-
-  return urls;
-}
-
-void Predictor::set_max_queueing_delay(int max_queueing_delay_ms) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-  g_max_queueing_delay_ms = max_queueing_delay_ms;
-}
-
-void Predictor::set_max_parallel_resolves(size_t max_parallel_resolves) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-  g_max_parallel_resolves = max_parallel_resolves;
-}
-
-void Predictor::ShutdownOnUIThread(PrefService* user_prefs) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-
-  SaveStateForNextStartupAndTrim(user_prefs);
-
+void Predictor::PredictFrameSubresources(const GURL& url) {
+  DCHECK_EQ(url.GetWithEmptyPath(), url);
+  // Add one pass through the message loop to allow current navigation to
+  // proceed.
   BrowserThread::PostTask(
       BrowserThread::IO,
       FROM_HERE,
-      base::Bind(&Predictor::Shutdown, base::Unretained(this)));
+      NewRunnableMethod(this, &Predictor::PrepareFrameSubresources, url));
 }
 
-// ---------------------- End UI methods. -------------------------------------
+void Predictor::PrepareFrameSubresources(const GURL& url) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
+  DCHECK_EQ(url.GetWithEmptyPath(), url);
+  Referrers::iterator it = referrers_.find(url);
+  if (referrers_.end() == it) {
+    // Only when we don't know anything about this url, make 2 connections
+    // available.  We could do this completely via learning (by prepopulating
+    // the referrer_ list with this expected value), but it would swell the
+    // size of the list with all the "Leaf" nodes in the tree (nodes that don't
+    // load any subresources).  If we learn about this resource, we will instead
+    // provide a more carefully estimated preconnection count.
+    if (preconnect_enabled_)
+      PreconnectOnIOThread(url, UrlInfo::SELF_REFERAL_MOTIVATED, 2);
+    return;
+  }
 
-// --------------------- Start IO methods. ------------------------------------
-
-void Predictor::Shutdown() {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-  DCHECK(!shutdown_);
-  shutdown_ = true;
-
-  STLDeleteElements(&pending_lookups_);
-}
-
-void Predictor::DiscardAllResults() {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-  // Delete anything listed so far in this session that shows in about:dns.
-  referrers_.clear();
-
-
-  // Try to delete anything in our work queue.
-  while (!work_queue_.IsEmpty()) {
-    // Emulate processing cycle as though host was not found.
-    GURL url = work_queue_.Pop();
-    UrlInfo* info = &results_[url];
-    DCHECK(info->HasUrl(url));
-    info->SetAssignedState();
-    info->SetNoSuchNameState();
+  Referrer* referrer = &(it->second);
+  referrer->IncrementUseCount();
+  const UrlInfo::ResolutionMotivation motivation =
+      UrlInfo::LEARNED_REFERAL_MOTIVATED;
+  for (Referrer::iterator future_url = referrer->begin();
+       future_url != referrer->end(); ++future_url) {
+    SubresourceValue evalution(TOO_NEW);
+    double connection_expectation = future_url->second.subresource_use_rate();
+    UMA_HISTOGRAM_CUSTOM_COUNTS("Net.PreconnectSubresourceExpectation",
+                                static_cast<int>(connection_expectation * 100),
+                                10, 5000, 50);
+    future_url->second.ReferrerWasObserved();
+    if (preconnect_enabled_ &&
+        connection_expectation > kPreconnectWorthyExpectedValue) {
+      evalution = PRECONNECTION;
+      future_url->second.IncrementPreconnectionCount();
+      int count = static_cast<int>(std::ceil(connection_expectation));
+      if (url.host() == future_url->first.host())
+        ++count;
+      PreconnectOnIOThread(future_url->first, motivation, count);
+    } else if (connection_expectation > kDNSPreresolutionWorthyExpectedValue) {
+      evalution = PRERESOLUTION;
+      future_url->second.preresolution_increment();
+      UrlInfo* queued_info = AppendToResolutionQueue(future_url->first,
+                                                     motivation);
+      if (queued_info)
+        queued_info->SetReferringHostname(url);
+    }
+    UMA_HISTOGRAM_ENUMERATION("Net.PreconnectSubresourceEval", evalution,
+                              SUBRESOURCE_VALUE_MAX);
   }
-  // Now every result_ is either resolved, or is being resolved
-  // (see LookupRequest).
-
-  // Step through result_, recording names of all hosts that can't be erased.
-  // We can't erase anything being worked on.
-  Results assignees;
-  for (Results::iterator it = results_.begin(); results_.end() != it; ++it) {
-    GURL url(it->first);
-    UrlInfo* info = &it->second;
-    DCHECK(info->HasUrl(url));
-    if (info->is_assigned()) {
-      info->SetPendingDeleteState();
-      assignees[url] = *info;
-    }
-  }
-  DCHECK_LE(assignees.size(), max_concurrent_dns_lookups_);
-  results_.clear();
-  // Put back in the names being worked on.
-  for (Results::iterator it = assignees.begin(); assignees.end() != it; ++it) {
-    DCHECK(it->second.is_marked_to_delete());
-    results_[it->first] = it->second;
-  }
-}
-
-// Overloaded Resolve() to take a vector of names.
-void Predictor::ResolveList(const UrlList& urls,
-                            UrlInfo::ResolutionMotivation motivation) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-
-  for (UrlList::const_iterator it = urls.begin(); it < urls.end(); ++it) {
-    AppendToResolutionQueue(*it, motivation);
-  }
-}
-
-// Basic Resolve() takes an invidual name, and adds it
-// to the queue.
-void Predictor::Resolve(const GURL& url,
-                        UrlInfo::ResolutionMotivation motivation) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-  if (!url.has_host())
-    return;
-  AppendToResolutionQueue(url, motivation);
-}
-
-void Predictor::LearnFromNavigation(const GURL& referring_url,
-                                    const GURL& target_url) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-  if (!predictor_enabled_)
-    return;
-  DCHECK_EQ(referring_url, Predictor::CanonicalizeUrl(referring_url));
-  DCHECK_NE(referring_url, GURL::EmptyGURL());
-  DCHECK_EQ(target_url, Predictor::CanonicalizeUrl(target_url));
-  DCHECK_NE(target_url, GURL::EmptyGURL());
-
-  referrers_[referring_url].SuggestHost(target_url);
-  // Possibly do some referrer trimming.
-  TrimReferrers();
-}
-
-//-----------------------------------------------------------------------------
-// This section supports the about:dns page.
-
-void Predictor::PredictorGetHtmlInfo(Predictor* predictor,
-                                     std::string* output) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-
-  output->append("<html><head><title>About DNS</title>"
-                 // We'd like the following no-cache... but it doesn't work.
-                 // "<META HTTP-EQUIV=\"Pragma\" CONTENT=\"no-cache\">"
-                 "</head><body>");
-  if (predictor && predictor->predictor_enabled()) {
-    predictor->GetHtmlInfo(output);
-  } else {
-    output->append("DNS pre-resolution and TCP pre-connection is disabled.");
-  }
-  output->append("</body></html>");
 }
 
 // Provide sort order so all .com's are together, etc.
 struct RightToLeftStringSorter {
   bool operator()(const GURL& left,
                   const GURL& right) const {
     return string_compare(left.host(), right.host());
   }
 
   static bool string_compare(const std::string& left_host,
@@ skipping 94 matching lines @@
           static_cast<int>(future_url->second.preresolution_count()),
           static_cast<double>(future_url->second.subresource_use_rate()),
           future_url->first.spec().c_str());
     }
   }
   output->append("</table>");
 }
 
 void Predictor::GetHtmlInfo(std::string* output) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-  if (initial_observer_.get())
-    initial_observer_->GetFirstResolutionsHtml(output);
-  // Show list of subresource predictions and stats.
-  GetHtmlReferrerLists(output);
-
   // Local lists for calling UrlInfo
   UrlInfo::UrlInfoTable name_not_found;
   UrlInfo::UrlInfoTable name_preresolved;
 
   // Get copies of all useful data.
   typedef std::map<GURL, UrlInfo, RightToLeftStringSorter> SortedUrlInfo;
   SortedUrlInfo snapshot;
   // UrlInfo supports value semantics, so we can do a shallow copy.
   for (Results::iterator it(results_.begin()); it != results_.end(); it++)
     snapshot[it->first] = it->second;
@@ skipping 15 matching lines @@
   brief = true;
 #endif  // NDEBUG
 
   // Call for display of each table, along with title.
   UrlInfo::GetHtmlTable(name_preresolved,
       "Preresolution DNS records performed for ", brief, output);
   UrlInfo::GetHtmlTable(name_not_found,
       "Preresolving DNS records revealed non-existence for ", brief, output);
 }
 
-void Predictor::TrimReferrersNow() {
+UrlInfo* Predictor::AppendToResolutionQueue(
+    const GURL& url,
+    UrlInfo::ResolutionMotivation motivation) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-  // Just finish up work if an incremental trim is in progress.
-  if (urls_being_trimmed_.empty())
-    LoadUrlsForTrimming();
-  IncrementalTrimReferrers(true);  // Do everything now.
+  DCHECK(url.has_host());
+
+  if (shutdown_)
+    return NULL;
+
+  UrlInfo* info = &results_[url];
+  info->SetUrl(url);  // Initialize or DCHECK.
+  // TODO(jar):  I need to discard names that have long since expired.
+  // Currently we only add to the domain map :-/
+
+  DCHECK(info->HasUrl(url));
+
+  if (!info->NeedsDnsUpdate()) {
+    info->DLogResultsStats("DNS PrefetchNotUpdated");
+    return NULL;
+  }
+
+  info->SetQueuedState(motivation);
+  work_queue_.Push(url, motivation);
+  StartSomeQueuedResolutions();
+  return info;
 }
 
-void Predictor::SerializeReferrers(base::ListValue* referral_list) {
+void Predictor::StartSomeQueuedResolutions() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-  referral_list->Clear();
-  referral_list->Append(new base::FundamentalValue(PREDICTOR_REFERRER_VERSION));
-  for (Referrers::const_iterator it = referrers_.begin();
-       it != referrers_.end(); ++it) {
-    // Serialize the list of subresource names.
-    Value* subresource_list(it->second.Serialize());
 
-    // Create a list for each referer.
-    ListValue* motivator(new ListValue);
-    motivator->Append(new StringValue(it->first.spec()));
-    motivator->Append(subresource_list);
+  while (!work_queue_.IsEmpty() &&
+         pending_lookups_.size() < max_concurrent_dns_lookups_) {
+    const GURL url(work_queue_.Pop());
+    UrlInfo* info = &results_[url];
+    DCHECK(info->HasUrl(url));
+    info->SetAssignedState();
 
-    referral_list->Append(motivator);
-  }
-}
+    if (CongestionControlPerformed(info)) {
+      DCHECK(work_queue_.IsEmpty());
+      return;
+    }
 
-void Predictor::DeserializeReferrers(const base::ListValue& referral_list) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-  int format_version = -1;
-  if (referral_list.GetSize() > 0 &&
-      referral_list.GetInteger(0, &format_version) &&
-      format_version == PREDICTOR_REFERRER_VERSION) {
-    for (size_t i = 1; i < referral_list.GetSize(); ++i) {
-      base::ListValue* motivator;
-      if (!referral_list.GetList(i, &motivator)) {
-        NOTREACHED();
-        return;
-      }
-      std::string motivating_url_spec;
-      if (!motivator->GetString(0, &motivating_url_spec)) {
-        NOTREACHED();
-        return;
-      }
-
-      Value* subresource_list;
-      if (!motivator->Get(1, &subresource_list)) {
-        NOTREACHED();
-        return;
-      }
-
-      referrers_[GURL(motivating_url_spec)].Deserialize(*subresource_list);
+    LookupRequest* request = new LookupRequest(this, host_resolver_, url);
+    int status = request->Start();
+    if (status == net::ERR_IO_PENDING) {
+      // Will complete asynchronously.
+      pending_lookups_.insert(request);
+      peak_pending_lookups_ = std::max(peak_pending_lookups_,
+                                       pending_lookups_.size());
+    } else {
+      // Completed synchronously (was already cached by HostResolver), or else
+      // there was (equivalently) some network error that prevents us from
+      // finding the name.  Status net::OK means it was "found."
+      LookupFinished(request, url, status == net::OK);
+      delete request;
     }
   }
 }
 
-void Predictor::DeserializeReferrersThenDelete(
-    base::ListValue* referral_list) {
-  DeserializeReferrers(*referral_list);
-  delete referral_list;
-}
-
-void Predictor::DiscardInitialNavigationHistory() {
+bool Predictor::CongestionControlPerformed(UrlInfo* info) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-  if (initial_observer_.get())
-    initial_observer_->DiscardInitialNavigationHistory();
-}
-
-void Predictor::FinalizeInitializationOnIOThread(
-    const UrlList& startup_urls,
-    base::ListValue* referral_list,
-    IOThread* io_thread) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-
-  initial_observer_.reset(new InitialObserver());
-  host_resolver_ = io_thread->globals()->host_resolver.get();
-
-  // ScopedRunnableMethodFactory instances need to be created and destroyed
-  // on the same thread. The predictor lives on the IO thread and will die
-  // from there so now that we're on the IO thread we need to properly
-  // initialize the ScopedrunnableMethodFactory.
-  trim_task_factory_.reset(new ScopedRunnableMethodFactory<Predictor>(this));
-
-  // Prefetch these hostnames on startup.
-  DnsPrefetchMotivatedList(startup_urls, UrlInfo::STARTUP_LIST_MOTIVATED);
-  DeserializeReferrersThenDelete(referral_list);
-}
-
-//-----------------------------------------------------------------------------
-// This section intermingles prefetch results with actual browser HTTP
-// network activity.  It supports calculating of the benefit of a prefetch, as
-// well as recording what prefetched hostname resolutions might be potentially
-// helpful during the next chrome-startup.
-//-----------------------------------------------------------------------------
-
-void Predictor::LearnAboutInitialNavigation(const GURL& url) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-  if (!predictor_enabled_ || NULL == initial_observer_.get() )
-    return;
-  initial_observer_->Append(url, this);
-}
-
-// This API is only used in the browser process.
-// It is called from an IPC message originating in the renderer.  It currently
-// includes both Page-Scan, and Link-Hover prefetching.
-// TODO(jar): Separate out link-hover prefetching, and page-scan results.
-void Predictor::DnsPrefetchList(const NameList& hostnames) {
-  // TODO(jar): Push GURL transport further back into renderer, but this will
-  // require a Webkit change in the observer :-/.
-  UrlList urls;
-  for (NameList::const_iterator it = hostnames.begin();
-       it < hostnames.end();
-       ++it) {
-    urls.push_back(GURL("http://" + *it + ":80"));
+  // Note: queue_duration is ONLY valid after we go to assigned state.
+  if (info->queue_duration() < max_dns_queue_delay_)
+    return false;
+  // We need to discard all entries in our queue, as we're keeping them waiting
+  // too long.  By doing this, we'll have a chance to quickly service urgent
+  // resolutions, and not have a bogged down system.
+  while (true) {
+    info->RemoveFromQueue();
+    if (work_queue_.IsEmpty())
+      break;
+    info = &results_[work_queue_.Pop()];
+    info->SetAssignedState();
   }
-
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-  DnsPrefetchMotivatedList(urls, UrlInfo::PAGE_SCAN_MOTIVATED);
-}
-
-void Predictor::DnsPrefetchMotivatedList(
-    const UrlList& urls,
-    UrlInfo::ResolutionMotivation motivation) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI) ||
-         BrowserThread::CurrentlyOn(BrowserThread::IO));
-  if (!predictor_enabled_)
-    return;
-
-  if (BrowserThread::CurrentlyOn(BrowserThread::IO)) {
-    ResolveList(urls, motivation);
-  } else {
-    BrowserThread::PostTask(
-        BrowserThread::IO,
-        FROM_HERE,
-        base::Bind(&Predictor::ResolveList, base::Unretained(this),
-                   urls, motivation));
-  }
-}
-
-//-----------------------------------------------------------------------------
-// Functions to handle saving of hostnames from one session to the next, to
-// expedite startup times.
-
-static void SaveDnsPrefetchStateForNextStartupAndTrimOnIOThread(
-    base::ListValue* startup_list,
-    base::ListValue* referral_list,
-    base::WaitableEvent* completion,
-    Predictor* predictor) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-
-  if (NULL == predictor) {
-    completion->Signal();
-    return;
-  }
-  predictor->SaveDnsPrefetchStateForNextStartupAndTrim(
-      startup_list, referral_list, completion);
-}
-
-void Predictor::SaveStateForNextStartupAndTrim(PrefService* prefs) {
-  if (!predictor_enabled_)
-    return;
-
-  base::WaitableEvent completion(true, false);
-
-  ListPrefUpdate update_startup_list(prefs, prefs::kDnsPrefetchingStartupList);
-  ListPrefUpdate update_referral_list(prefs,
-                                      prefs::kDnsPrefetchingHostReferralList);
-  if (BrowserThread::CurrentlyOn(BrowserThread::IO)) {
-    SaveDnsPrefetchStateForNextStartupAndTrimOnIOThread(
-        update_startup_list.Get(),
-        update_referral_list.Get(),
-        &completion,
-        this);
-  } else {
-    bool posted = BrowserThread::PostTask(
-        BrowserThread::IO,
-        FROM_HERE,
-        base::Bind(
-            SaveDnsPrefetchStateForNextStartupAndTrimOnIOThread,
-            update_startup_list.Get(),
-            update_referral_list.Get(),
-            &completion,
-            this));
-
-    // TODO(jar): Synchronous waiting for the IO thread is a potential source
-    // to deadlocks and should be investigated. See http://crbug.com/78451.
-    DCHECK(posted);
-    if (posted)
-      completion.Wait();
-  }
-}
-
-void Predictor::SaveDnsPrefetchStateForNextStartupAndTrim(
-    base::ListValue* startup_list,
-    base::ListValue* referral_list,
-    base::WaitableEvent* completion) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-  if (initial_observer_.get())
-    initial_observer_->GetInitialDnsResolutionList(startup_list);
-
-  // Do at least one trim at shutdown, in case the user wasn't running long
-  // enough to do any regular trimming of referrers.
-  TrimReferrersNow();
-  SerializeReferrers(referral_list);
-
-  completion->Signal();
-}
-
-void Predictor::EnablePredictor(bool enable) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI) ||
-         BrowserThread::CurrentlyOn(BrowserThread::IO));
-
-  if (BrowserThread::CurrentlyOn(BrowserThread::IO)) {
-    EnablePredictorOnIOThread(enable);
-  } else {
-    BrowserThread::PostTask(
-        BrowserThread::IO,
-        FROM_HERE,
-        base::Bind(&Predictor::EnablePredictorOnIOThread,
-                   base::Unretained(this), enable));
-  }
-}
-
-void Predictor::EnablePredictorOnIOThread(bool enable) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-  predictor_enabled_ = enable;
-}
-
-void Predictor::PredictFrameSubresources(const GURL& url) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI) ||
-         BrowserThread::CurrentlyOn(BrowserThread::IO));
-  if (!predictor_enabled_)
-    return;
-  DCHECK_EQ(url.GetWithEmptyPath(), url);
-  // Add one pass through the message loop to allow current navigation to
-  // proceed.
-  if (BrowserThread::CurrentlyOn(BrowserThread::IO)) {
-    PrepareFrameSubresources(url);
-  } else {
-    BrowserThread::PostTask(
-        BrowserThread::IO,
-        FROM_HERE,
-        base::Bind(&Predictor::PrepareFrameSubresources,
-                   base::Unretained(this), url));
-  }
-}
-
-enum SubresourceValue {
-  PRECONNECTION,
-  PRERESOLUTION,
-  TOO_NEW,
-  SUBRESOURCE_VALUE_MAX
-};
-
-void Predictor::PrepareFrameSubresources(const GURL& url) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-  DCHECK_EQ(url.GetWithEmptyPath(), url);
-  Referrers::iterator it = referrers_.find(url);
-  if (referrers_.end() == it) {
-    // Only when we don't know anything about this url, make 2 connections
-    // available.  We could do this completely via learning (by prepopulating
-    // the referrer_ list with this expected value), but it would swell the
-    // size of the list with all the "Leaf" nodes in the tree (nodes that don't
-    // load any subresources).  If we learn about this resource, we will instead
-    // provide a more carefully estimated preconnection count.
-    if (preconnect_enabled_)
-      PreconnectOnIOThread(url, UrlInfo::SELF_REFERAL_MOTIVATED, 2);
-    return;
-  }
-
-  Referrer* referrer = &(it->second);
-  referrer->IncrementUseCount();
-  const UrlInfo::ResolutionMotivation motivation =
-      UrlInfo::LEARNED_REFERAL_MOTIVATED;
-  for (Referrer::iterator future_url = referrer->begin();
-       future_url != referrer->end(); ++future_url) {
-    SubresourceValue evalution(TOO_NEW);
-    double connection_expectation = future_url->second.subresource_use_rate();
-    UMA_HISTOGRAM_CUSTOM_COUNTS("Net.PreconnectSubresourceExpectation",
-                                static_cast<int>(connection_expectation * 100),
-                                10, 5000, 50);
-    future_url->second.ReferrerWasObserved();
-    if (preconnect_enabled_ &&
-        connection_expectation > kPreconnectWorthyExpectedValue) {
-      evalution = PRECONNECTION;
-      future_url->second.IncrementPreconnectionCount();
-      int count = static_cast<int>(std::ceil(connection_expectation));
-      if (url.host() == future_url->first.host())
-        ++count;
-      PreconnectOnIOThread(future_url->first, motivation, count);
-    } else if (connection_expectation > kDNSPreresolutionWorthyExpectedValue) {
-      evalution = PRERESOLUTION;
-      future_url->second.preresolution_increment();
-      UrlInfo* queued_info = AppendToResolutionQueue(future_url->first,
-                                                     motivation);
-      if (queued_info)
-        queued_info->SetReferringHostname(url);
-    }
-    UMA_HISTOGRAM_ENUMERATION("Net.PreconnectSubresourceEval", evalution,
-                              SUBRESOURCE_VALUE_MAX);
-  }
+  return true;
 }
 
 void Predictor::OnLookupFinished(LookupRequest* request, const GURL& url,
                                  bool found) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
 
   LookupFinished(request, url, found);
   pending_lookups_.erase(request);
   delete request;
 
   StartSomeQueuedResolutions();
 }
 
 void Predictor::LookupFinished(LookupRequest* request, const GURL& url,
                                bool found) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
   UrlInfo* info = &results_[url];
   DCHECK(info->HasUrl(url));
   if (info->is_marked_to_delete()) {
     results_.erase(url);
   } else {
     if (found)
       info->SetFoundState();
     else
       info->SetNoSuchNameState();
   }
 }
 
-UrlInfo* Predictor::AppendToResolutionQueue(
-    const GURL& url,
-    UrlInfo::ResolutionMotivation motivation) {
+void Predictor::DiscardAllResults() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-  DCHECK(url.has_host());
+  // Delete anything listed so far in this session that shows in about:dns.
+  referrers_.clear();
 
-  if (shutdown_)
-    return NULL;
 
-  UrlInfo* info = &results_[url];
-  info->SetUrl(url);  // Initialize or DCHECK.
-  // TODO(jar):  I need to discard names that have long since expired.
-  // Currently we only add to the domain map :-/
-
-  DCHECK(info->HasUrl(url));
-
-  if (!info->NeedsDnsUpdate()) {
-    info->DLogResultsStats("DNS PrefetchNotUpdated");
-    return NULL;
-  }
-
-  info->SetQueuedState(motivation);
-  work_queue_.Push(url, motivation);
-  StartSomeQueuedResolutions();
-  return info;
-}
-
-bool Predictor::CongestionControlPerformed(UrlInfo* info) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-  // Note: queue_duration is ONLY valid after we go to assigned state.
-  if (info->queue_duration() < max_dns_queue_delay_)
-    return false;
-  // We need to discard all entries in our queue, as we're keeping them waiting
-  // too long.  By doing this, we'll have a chance to quickly service urgent
-  // resolutions, and not have a bogged down system.
-  while (true) {
-    info->RemoveFromQueue();
-    if (work_queue_.IsEmpty())
-      break;
-    info = &results_[work_queue_.Pop()];
-    info->SetAssignedState();
-  }
-  return true;
-}
-
-void Predictor::StartSomeQueuedResolutions() {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-
-  while (!work_queue_.IsEmpty() &&
-         pending_lookups_.size() < max_concurrent_dns_lookups_) {
-    const GURL url(work_queue_.Pop());
+  // Try to delete anything in our work queue.
+  while (!work_queue_.IsEmpty()) {
+    // Emulate processing cycle as though host was not found.
+    GURL url = work_queue_.Pop();
     UrlInfo* info = &results_[url];
     DCHECK(info->HasUrl(url));
     info->SetAssignedState();
+    info->SetNoSuchNameState();
+  }
+  // Now every result_ is either resolved, or is being resolved
+  // (see LookupRequest).
 
-    if (CongestionControlPerformed(info)) {
-      DCHECK(work_queue_.IsEmpty());
-      return;
+  // Step through result_, recording names of all hosts that can't be erased.
+  // We can't erase anything being worked on.
+  Results assignees;
+  for (Results::iterator it = results_.begin(); results_.end() != it; ++it) {
+    GURL url(it->first);
+    UrlInfo* info = &it->second;
+    DCHECK(info->HasUrl(url));
+    if (info->is_assigned()) {
+      info->SetPendingDeleteState();
+      assignees[url] = *info;
     }
+  }
+  DCHECK(assignees.size() <= max_concurrent_dns_lookups_);
+  results_.clear();
+  // Put back in the names being worked on.
+  for (Results::iterator it = assignees.begin(); assignees.end() != it; ++it) {
+    DCHECK(it->second.is_marked_to_delete());
+    results_[it->first] = it->second;
+  }
+}
 
-    LookupRequest* request = new LookupRequest(this, host_resolver_, url);
-    int status = request->Start();
-    if (status == net::ERR_IO_PENDING) {
-      // Will complete asynchronously.
-      pending_lookups_.insert(request);
-      peak_pending_lookups_ = std::max(peak_pending_lookups_,
-                                       pending_lookups_.size());
-    } else {
-      // Completed synchronously (was already cached by HostResolver), or else
-      // there was (equivalently) some network error that prevents us from
-      // finding the name.  Status net::OK means it was "found."
-      LookupFinished(request, url, status == net::OK);
-      delete request;
+void Predictor::TrimReferrersNow() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
+  // Just finish up work if an incremental trim is in progress.
+  if (urls_being_trimmed_.empty())
+    LoadUrlsForTrimming();
+  IncrementalTrimReferrers(true);  // Do everything now.
+}
+
+void Predictor::SerializeReferrers(ListValue* referral_list) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
+  referral_list->Clear();
+  referral_list->Append(new base::FundamentalValue(PREDICTOR_REFERRER_VERSION));
+  for (Referrers::const_iterator it = referrers_.begin();
+       it != referrers_.end(); ++it) {
+    // Serialize the list of subresource names.
+    Value* subresource_list(it->second.Serialize());
+
+    // Create a list for each referer.
+    ListValue* motivator(new ListValue);
+    motivator->Append(new StringValue(it->first.spec()));
+    motivator->Append(subresource_list);
+
+    referral_list->Append(motivator);
+  }
+}
+
+void Predictor::DeserializeReferrers(const ListValue& referral_list) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
+  int format_version = -1;
+  if (referral_list.GetSize() > 0 &&
+      referral_list.GetInteger(0, &format_version) &&
+      format_version == PREDICTOR_REFERRER_VERSION) {
+    for (size_t i = 1; i < referral_list.GetSize(); ++i) {
+      ListValue* motivator;
+      if (!referral_list.GetList(i, &motivator)) {
+        NOTREACHED();
+        return;
+      }
+      std::string motivating_url_spec;
+      if (!motivator->GetString(0, &motivating_url_spec)) {
+        NOTREACHED();
+        return;
+      }
+
+      Value* subresource_list;
+      if (!motivator->Get(1, &subresource_list)) {
+        NOTREACHED();
+        return;
+      }
+
+      referrers_[GURL(motivating_url_spec)].Deserialize(*subresource_list);
     }
   }
 }
 
 void Predictor::TrimReferrers() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
   if (!urls_being_trimmed_.empty())
     return;   // There is incremental trimming in progress already.
 
   // Check to see if it is time to trim yet.
@@ skipping 12 matching lines @@
        it != referrers_.end(); ++it)
     urls_being_trimmed_.push_back(it->first);
   UMA_HISTOGRAM_COUNTS("Net.PredictionTrimSize", urls_being_trimmed_.size());
 }
 
 void Predictor::PostIncrementalTrimTask() {
   if (urls_being_trimmed_.empty())
     return;
   MessageLoop::current()->PostDelayedTask(
       FROM_HERE,
-      trim_task_factory_->NewRunnableMethod(
-          &Predictor::IncrementalTrimReferrers, false),
+      trim_task_factory_.NewRunnableMethod(&Predictor::IncrementalTrimReferrers,
+                                           false),
       kDurationBetweenTrimmingIncrements.InMilliseconds());
 }
 
 void Predictor::IncrementalTrimReferrers(bool trim_all_now) {
   size_t trim_count = urls_being_trimmed_.size();
   if (!trim_all_now)
     trim_count = std::min(trim_count, kUrlsTrimmedPerIncrement);
   while (trim_count-- != 0) {
     Referrers::iterator it = referrers_.find(urls_being_trimmed_.back());
     urls_being_trimmed_.pop_back();
     if (it == referrers_.end())
       continue;  // Defensive code: It got trimmed away already.
     if (!it->second.Trim(kReferrerTrimRatio, kDiscardableExpectedValue))
       referrers_.erase(it);
   }
   PostIncrementalTrimTask();
 }
 
-// ---------------------- End IO methods. -------------------------------------
-
-//-----------------------------------------------------------------------------
+//------------------------------------------------------------------------------
 
 Predictor::HostNameQueue::HostNameQueue() {
 }
 
 Predictor::HostNameQueue::~HostNameQueue() {
 }
 
 void Predictor::HostNameQueue::Push(const GURL& url,
     UrlInfo::ResolutionMotivation motivation) {
   switch (motivation) {
@@ skipping 15 matching lines @@
 
 GURL Predictor::HostNameQueue::Pop() {
   DCHECK(!IsEmpty());
   std::queue<GURL> *queue(rush_queue_.empty() ? &background_queue_
                                               : &rush_queue_);
   GURL url(queue->front());
   queue->pop();
   return url;
 }
 
-//-----------------------------------------------------------------------------
-// Member definitions for InitialObserver class.
-
-Predictor::InitialObserver::InitialObserver() {
+void Predictor::DeserializeReferrersThenDelete(ListValue* referral_list) {
+    DeserializeReferrers(*referral_list);
+    delete referral_list;
 }
 
-Predictor::InitialObserver::~InitialObserver() {
-}
 
-void Predictor::InitialObserver::Append(const GURL& url,
-                                        Predictor* predictor) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-
-  // TODO(rlp): Do we really need the predictor check here?
-  if (NULL == predictor)
-    return;
-  if (kStartupResolutionCount <= first_navigations_.size())
-    return;
-
-  DCHECK(url.SchemeIs("http") || url.SchemeIs("https"));
-  DCHECK_EQ(url, Predictor::CanonicalizeUrl(url));
-  if (first_navigations_.find(url) == first_navigations_.end())
-    first_navigations_[url] = base::TimeTicks::Now();
-}
-
-void Predictor::InitialObserver::GetInitialDnsResolutionList(
-    base::ListValue* startup_list) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-  DCHECK(startup_list);
-  startup_list->Clear();
-  DCHECK_EQ(0u, startup_list->GetSize());
-  startup_list->Append(
-      new base::FundamentalValue(kPredictorStartupFormatVersion));
-  for (FirstNavigations::iterator it = first_navigations_.begin();
-       it != first_navigations_.end();
-       ++it) {
-    DCHECK(it->first == Predictor::CanonicalizeUrl(it->first));
-    startup_list->Append(new StringValue(it->first.spec()));
-  }
-}
-
-void Predictor::InitialObserver::GetFirstResolutionsHtml(
-    std::string* output) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-
-  UrlInfo::UrlInfoTable resolution_list;
-  {
-    for (FirstNavigations::iterator it(first_navigations_.begin());
-         it != first_navigations_.end();
-         it++) {
-      UrlInfo info;
-      info.SetUrl(it->first);
-      info.set_time(it->second);
-      resolution_list.push_back(info);
-    }
-  }
-  UrlInfo::GetHtmlTable(resolution_list,
-      "Future startups will prefetch DNS records for ", false, output);
-}
-
-//-----------------------------------------------------------------------------
+//------------------------------------------------------------------------------
 // Helper functions
-//-----------------------------------------------------------------------------
+//------------------------------------------------------------------------------
 
 // static
 GURL Predictor::CanonicalizeUrl(const GURL& url) {
   if (!url.has_host())
      return GURL::EmptyGURL();
 
   std::string scheme;
   if (url.has_scheme()) {
     scheme = url.scheme();
     if (scheme != "http" && scheme != "https")
       return GURL::EmptyGURL();
     if (url.has_port())
       return url.GetWithEmptyPath();
   } else {
     scheme = "http";
   }
 
   // If we omit a port, it will default to 80 or 443 as appropriate.
   std::string colon_plus_port;
   if (url.has_port())
     colon_plus_port = ":" + url.port();
 
   return GURL(scheme + "://" + url.host() + colon_plus_port);
 }
 
-void SimpleShutdownPredictor::ShutdownOnUIThread(PrefService* user_prefs) {
-  SetShutdown(true);
-}
 
 }  // namespace chrome_browser_net